Release for electric switches or stops for motors



Dec. 8, 1925. 1,564,377

M. c. SPENCER RELEASE FOR ELECTRIC SWITCHES 0R STOPS FOR MOTORS Filed Nov. 5, 1920 low Ila IZcb Fig. 1.

Inventor, Millard Cole 8 encer,

' Attorney- Patented Dec. 8, 1925.

atest? UNITED STATES PATENT @Fffifir...

MILLARD COLE SPENCER, 0F EAST GRANGE, NEE-V JERSEY, ASSIGNOR 'IO OROCKER- -J J'IZ 'EEILEB. COMPANY, OF AMPEBE, NEE V JERSEY, A CORPORATION OF NEW JERSEY.

RELEASE FOR ELECTRIC SWITCHES 0E STOPS FOR, MOTORS.

Application filed November 5, 1920.

Z '0 (M whom it may concern:

Be it known that L MrLLAnD CoLn SPENCER, a citizen of the United States, residing at East Orange, county of Essex, and State of New Jersey, have invented certain new and useful Improvements in Releases for Electric Switches or Stops for Motors, of which the following is a specification.

This invention relates to releases for electric switches or stops for motors for delaying for a few seconds the action of a relay which is actuated by any overload in the circuitof the motor, and thus closes the secondary circuit, which puts into operation the means of stopping the motor.

here induction or synchronous motors or otherelec-trical devices are liable to heavy overloads itis necessary to protect them, and

in order to prevent their operation by momentary overloads it has been found advisable to introduce a time element. An electric motor is capable of carrying, momentarily, heavy overloads without injury, and from the point of view of the motor user, it is desirable that such momentary overloads should not trip the protective device and cause the motor to stop. All that is required of the protective device is that it shall not permit the overload to remain on the motor for a length of time sufficient to cause it to overheat,--say, over thirty seconds. In the case of the usual relay, this delay action is obtained by means of a dash-pot. One of the objects of the present invention is to overcome the disadvantages of, and objections to, a daslrpot, for, in order to make its operation reliable and to obtain sufficient delay action, it is necessary that the relay parts shall be made fairly large and heavy, and that the relay plunger shall travel through a considerable distance. Also, in order that the delay action shall be satisfactory, it is necessary that the dash-pot with its piston shall be nicely made and accurately fitted, all of which tends to make the device expensive. The use of a dash-pot also causes possible trouble, due to leakage of oil, and another object of this invention is to avoid such trouble. Other objects are to provide a substitute, which can be made much smaller, more compact and less expensive than the usual large and expensive relay and bulky dash-pot.

These being among the objects of the present invention,-other objects of which will Serial No. 421,904.

appear hereinthe same consists of certain features of construction and combinations of parts to be hereinafter described and then claimed with reference to the accompanying drawing illustrating a desirable embodiment of the invention, in which Fig. 1 is a front elevation of apparatus involving the invention, which is adapted for alternating current, and which is conveniently mounted upon a switchboard;

Fig. 2 is a side view of the apparatus; and

Fig. 3 is a detail top plan of the switchlocking means.

Referring to the drawings, 10, 11, 12 illustrate the knives of a knife-switch for al ternating current motors. The mains 10-, 11 12 closed by the knife-switches, comprise the fined contacts 14, for the knifeswitches, the switch parts be ng mounted upon a slate, marble, or other suitable slab 15. Circuits 13, 13 are connected up with the means, and in them are located the con tacts 16, 16, for small relay magnets 1?, 1%, which have armatures 0r plungers 1 18 The magnets of the relays are shown in the form of solenoids, but any other suitable type of magnets may be employed.

mall metallic washers 19, 19, are arranged loosely on the plungers 18, 18*, and rest upon buffer-spring 20, 20 suitably held in position. These washers constitute the switches of the relays, for closing the shunt circuits 13, 13*, atcontacts 16, 16.

Shunt-circuits 21, 21 are connected across the resistances 22, 22, for energizing the coils of the relay-magnets 17, 17 The resistances 22, 22 may each be a short length of wire, or a strip of sheet metal, and each -is connected in series with the circuit to be protected. Thig wire or strip is preferably composed of iron, although other metals might be used. Each shunt-circuit 21, 21 is in parallel with its corresponding res1stance.

By means of the described device, the desired delay action is obtained by the heating up of the short length of wire or strip 22, or 22 and it is obvious that the greater the resistance of the said wire, with respect to the impedance of the corresponding relay-coil, the greater will be the portion of the line current which flows through the coil. The length of wire or strip 22, or 22, is so designed that, at the temperature to which it is heated by the current which flows througlrit when the motor is carrying slightly more than the maximum overload which it is capable of carrying continuously without injury, it causes to flow through the corresponding relay-coil just sufiicient current to operate the. relay, vhich closes the relay and stops the motor. The desired delay action is caused by the fact that. the electrical resistance of the wire, 22 or 22 *hich increases rapidly with its temperature, does not reach a value which is high enough to send a sui'iiciently large portion of the line current through the corresponding relay to operate ituntil the wire has been raised to a fairly high temperature. It is this length of time required to heat the wire by the current flowing tl'irough it that causes the desired delay action. When the current first starts to how, and the wire is cold, its resistance is low, and a large portion the line current flows through the w e, and a small portion through the relay. the wire heats up its resistance increases and agrcater portion of the line current is for :ed through the relay until, it the line current is great enough, the relay is operated and the switch 19 or 19 is closed. It is obvious that the greater the line current, or the greater the overload of the motor, the greater will be the current flowing through the wire, and the sooner it will heat up to a ten'iperature which will increase its resistance sutliciently to force enough current through the relay to cause it to operate. This is exactly the characteristic desired; that is, the greater the overload, the lessthe time the motor should be permitted to carryit.

The means forlocking the knife-switch maybe simple, and such simple means is shown. The bar 23 of the said switch has an arn'iature 24-, which is under the control of the pole-piece 25, of a magnet 26. Said armature and pole-piece are laminated, for alternating current. The. circuit 27 of the holding magnet 26 is connected with mains ll, 12-? through an impedanceQT, so that normally the. magnet is energized Nhen, however, either or the relay-switches;v 19, 19, is closed, the holding magnet 26 is iii:

short-circuited and de-eiiergized, so that the weight 28 on the knife-switch will break the main circuit at 14, and the motor will stop. The object of the impedance 2? is to limit the current drawn from the line when the relay switcheslfl, 19 are closed.

It is obvious that a number of advantages are gained by the described apparatus, namely, the large, bulky, accurately made and expensive dash-pot of the usual, relay device is replaced by a simple, compact and inexpensive length of metallic wire or narrow strip of sheet metal, Jreterably iron. \Vith the use'of avresistance wire, such as 22, 22, the relay has only to either close or open an electric circuit, which can be done with a very small movenientct',say, onesixteenth of an inch, whereas, the usual type oi": relay must operate a dash-pot which requires a considerable movement, say, one half of an inch, hence, the relay for use with a resistance wire canbe made much smaller, more compact, and less expensive It is obvious that the parts of the present invention are susceptible of .niore or less modification, as parts may be omitted, parts added and parts altered, without changing the character and scope of the present invention as defined in the claim.

lVhat I claim as n'ewis:

In a release for electric switches, a main circuit, a conductor in the main circuit having the property of increasing in resistance when heated, a relay magnet in a shunt around the conductor and the action of which is delayed by the said conductor, a self-opening switch connected with the main circuit, a holding magnet for restraining said switch from opening and having a circuit connected with the main circuit, and. a normally open relay switchin shunt with the holding magnet circuitand closed by the relay magnet when the said conductor is sufficiently heated tot'orceenough current through the relay magnet to cause it to 0prfate therelay. switch, thereby-,short-circuiting said, holding magnet and de energizing it so as to release the self-opening switch.

MILLAR-D Conn srnncnn. 

